docs: def resolve_imports(self, imports, import_depth, parser=None):
          """Import required ontologies.
          """
          if imports and import_depth:
              for i in list(self.imports):
                  try:
  
                      if os.path.exists(i) or i.startswith(('http', 'ftp')):
                          self.merge(Ontology(i, import_depth=import_depth-1, parser=parser))
  
                      else: # try to look at neighbouring ontologies
                          self.merge(Ontology( os.path.join(os.path.dirname(self.path), i),
                                               import_depth=import_depth-1, parser=parser))
  
                  except (IOError, OSError, URLError, HTTPError, _etree.ParseError) as e:
                      warnings.warn("{} occured during import of "
                                    "{}".format(type(e).__name__, i),
                                    ProntoWarning)